To assess the association between coffee consumption and mortality from cardiovascular disease (CVD), cancer, and all causes during 18 years of follow-up in men and 24 years of follow-up in women.

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Provide a general description of the methods as reported by the authors. Information should be extracted based on relevance to the SR (i.e., caffeine related methods)

Study population: The Health Professionals Follow-up Study (HPFS) was established in 1986 and the Nurses' Health Study (NHS) in 1976. Information on the cohorts, except diet, has been updated every 2 years. Further details have been published elsewhere. We used 1980 as baseline for the NHS because this was the first year in which dietary information was collected in this cohort. In this study, after excluding participants with CVD or cancer at baseline or without information about coffee consumption at baseline (1183 persons in the HPFS and 879 in the NHS), we included in the analyses 41,736 men and 86,214 women who were followed until 2004.
Assessment of coffee consumption: Dietary questionnaires were sent to the HPFS participants in 1986, 1990, 1994, and 1998 and to the NHS participants in 1980, 1984, 1986, 1990, 1994, and 1998. In each questionnaire, participants were asked how often on average during the previous year they had consumed coffee and tea. The participants could choose from 9 responses. Decaffeinated coffee and different types of caffeinated soft drinks were first assessed in 1986 in the HPFS and in 1984 in the NHS. In addition, we also inquired at baseline if the participant's consumption for each beverage had greatly increased or decreased over the preceding 10 years. Using the U.S. Department of Agriculture food composition sources, supplemented with other sources, we estimated that the caffeine content was 137 mg per cup of coffee, 47 mg per cup of tea, 46 mg per can or a 12-ounce bottle of soft drink, and 7 mg per 1-ounce serving of chocolate candy. We assessed the total intake of caffeine by summing the caffeine content for a unit of each food during the previous year multiplied by a weight proportional to the frequency of its consumption.
Assessment of mortality: Deaths were reported by the next of kin or the postal authorities or were ascertained through the National Death Index. We estimated that follow-up for deaths was more than 98 percent complete. For all deaths, we sought death certificates and, when appropriate, requested permission from the next of kin to review medical records. The underlying cause of death was assigned according to the International Classification of Diseases, 8th Revision (ICD-8). The primary end point in this analysis was death for any cause. We also conducted analyses according to the main causes of deaths in the cohorts, which were CVD (ICD-8 codes 390.0 through 458.9 and 795.0 to 795.9).
Assessment of medical history and lifestyle factors: In the baseline questionnaires, we requested information about age, weight and height, smoking status, parental history with respect to myocardial infarction, menopausal status and use of hormone therapy in women, and personal history of hypertension, hypercholesterolemia, and type 2 diabetes mellitus. This information, with the exception of height and parental history, has been updated in the biennial follow-up questionnaires. In the HPFS, participants were queried about the average time spent per week during the preceding year in specific activities (e.g., walking outdoors, jogging, and bicycling). The time spent in each activity in hours per week was multiplied by its typical energy expenditure, expressed in metabolic equivalent tasks and then summed over all activities to yield a metabolic equivalent task/hour score. In the NHS, physical activity was reported in hours per week of moderate (e.g., brisk walking) and vigorous exercise (e.g., strenuous sports and jogging). (17) Standard portion sizes for alcoholic drinks were specified as a can/bottle or glass for beer, 4-oz glass for wine, and one drink or shot for liquor. Detailed information on the validity and reproducibility of the information about self-reported weight, physical activity, and alcohol consumption from the questionnaires has been reported elsewhere.

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How many outcome-specific endpoints are evaluated?

1

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What is the (or one of the) endpoint(s) evaluated? (Each endpoint listed separately)

Cardiovascular disease mortality

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List additional health endpoints (separately). 2

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List additional health endpoints (separately).3

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List additional health endpoints (separately).4

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List additional health endpoints (separately).5

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List additional health endpoints (separately).6

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Clinical, physiological, other

Clinical

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What is the study design?

Cohort

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Randomized or Non-Randomized?

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What were the diagnostics or methods used to measure the outcome?

Objective

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Optional: Name of Method or short description

Used National Death Index, next of kin, or postal authorities for information. Death certificates were sought for all deaths. Cause of death were coded based on ICD-8.

What was the reference, comparison, or control group(s)? (e.g. high vs low consumption, number of cups, etc.)

Less than 1 cup per month (reference group).

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What were the listed confounders or modifying factors as stated by the authors? (e.g. multi-variable components of models. Copy from methods)

Participants were classified according to levels of coffee consumption. To reduce within-subject variation and best represent long-term diet, we used the cumulative average of coffee consumption from all available dietary questionnaires up to the start of each 2-year follow-up interval; for example, in the HPFS, the average of the 1986 and 1990 intake was used for the follow-up between 1990 and 1994; and the average of the 1986, 1990, and 1994 intake was used for the follow-up between 1994 and 1998. When a food frequency questionnaire had a missing value for coffee, we used the value from the previous questionnaire.
Sex-specific Cox proportional hazards models were used to investigate the association between coffee consumption and incidence of death from all causes and specific mortality. To control as finely as possible for confounding by age and calendar time, we stratified the analysis jointly by age in months at start of follow-up and calendar year of the current questionnaire cycle. Hazard ratios were used to estimate relative risks in each category in comparison with participants in the lower category of coffee consumption. Multivariable models were adjusted for smoking status, body mass index, physical activity, alcohol intake, use of hormone therapy for women, parental history of myocardial infarction, and dietary factors (total energy intake, use of multivitamin and vitamin E supplements, polyunsaturated, saturated, n-3, and trans fat intake, glycemic load, and folic acid intake), by using categorical variables. To test for linear trends across categories, we modeled coffee consumption as a continuous variable using the median value of each level of coffee consumption. In addition, we calculated pooled relative risks of all cause mortality for men and women combined across categories of coffee consumption using a random effect method. We also examined a possible non-linear relation between coffee consumption and total and cardiovascular mortality non-parametrically with restricted cubic splines.
Stratified analyses were conducted according to smoking status, alcohol consumption, and body mass index. We examined interactions between coffee and the categories of the stratification variables with mortality using likelihood-ratio tests, which compared the nested models with and without cross-product terms. We also analyzed the independent effect of total coffee consumption compared to caffeine intake on mortality through cross-classifications of both variables. Finally, we examined the association between decaffeinated coffee consumption and mortality.
In secondary analyses, we controlled the association between coffee consumption and mortality for hypertension, hypercholesterolemia, diabetes (these diseases could modify coffee consumption) and perceived health. Moreover, we analyzed the association between continuous baseline coffee consumption and mortality, correcting the relative risk obtained using the method of Rosner et al.

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What conflicts of interest were reported?

Authors stated, "The founding sources had no role in the design and conduct of the study, analysis or interpretation of the data, or preparation or final approval of the manuscript before publication."

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Refid

18559841

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What were the sources of funding?

Supported by NIH research grants CA87969, CA55075, HL34594, and HL60712. Dr. Lopez-Garcia's research is supported by a ‘Ramón y Cajal’ contract. Dr. Hu's research is partly supported by an American Heart Association Established Investigator Award.

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Results & Comparisons

No Results found.

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